Harvard is perhaps the most prestigious University in the USA. The University was founded in 1636 in Cambridge Massachusetts, way before the USA became independent from Britain. The name came after John Harvard, a young minister, a graduate of Cambridge, England, who upon his death left library and estate to support the early time of University.

Before 20th century, European countries dominated the world and finest Universities such as Cambridge and Oxford were found in Europe.
However, because of World War I and II, European countries lost world power and the power shifted to the USA. Political and economic power shifts also made opportunity for American Universities to set the highest standards.

Harvard is like a huge cooperation or enterprise, investing in stocks, lands, not only investments in educations. Harvard's strong power is perhaps its prestigious name and also enormous financial power that could recruit the already established best star scholars in the world to be Harvard professors. Average assistant and associate professors are high standards in their levels. However, the presence of several, but not all, star professors at Harvard is making Harvard almost incomparable unique University.
In addition, Harvard-MIT, both located in Boston, perhaps two top Universities, have exchange programs that add more opportunities.
Learning from top professors naturally gives opportunities to students to stand in the front positions in the world in their fields.

You know, most of the star professors at Harvard are not necessarily graduates of these schools.